Conventionally, a three-phase alternating current arc furnace in which arcs are produced between a metal material in a furnace shell and three electrodes inserted into the furnace shell to melt the metal material by arc heat is widely used as a melting furnace for melting metal materials such as metal scrap.
In an operation of melting a metal material using such an electric arc furnace, conventionally, a scrap bucket is widely used as a means for charging the metal material into the furnace shell.
FIGS. 9A and 9B schematically illustrate a situation in which the metal material is charged into the furnace shell.
A reference numeral 201 represents a scrap bucket which has a circular cylindrical trunk portion 202 as a body in an upper portion, and an opening-and-closing door 203 that is opened while being split in half at the center to either side in a bottom portion.
A metal material is charged into an electric arc furnace 205 in such a manner that the metal material is put into the scrap bucket 201, this is conveyed to a position above the electric arc furnace 205, and the opening-and-closing door 203 on the bottom portion is opened by being split in half at the center to either side.
At this time, the metal material in the scrap bucket 201 falls downwards via an opening that is formed by opening the opening-and-closing door 203 on the bottom portion, and is charged into a furnace shell below the scrap bucket 201.
A metal material may contain a powdery material.
For example, in a case where a scrap material such as ferrous scrap is used as the metal material, the scrap material may contain a large plate-like scrap, or a fine powdery scrap.
The powdery scrap may include metal cutting chips such as lathe chips, or scrap that is produced by pulverizing the metal cutting chips further finely.
In the case where a metal material contains such a powdery material, the powdery metal material is likely to sink down to the bottom in the scrap bucket, to move to a seam 204 at a tip end of the half split opening-and-closing door 203 and the vicinity thereof, to gather therearound.
In this case, when the opening-and-closing door 203 on the bottom portion of the scrap bucket 201 is opened into two pieces so as to charge the metal material into a furnace shell 206 of the electric arc furnace 205, the powdery material, which gathers in the vicinity of the seam 204 at the tip end of the opening-and-closing door 203, falls downwards into the furnace shell 206 while spreading via a slit that is formed by an opening operation of the opening-and-closing door 203, that is, a gap (that is, an opening with a narrow width at an initial time of opening).
In this case, if an extension direction of the seam 204 of the half split opening-and-closing door 203 of the scrap bucket 201, that is, an extension direction of a tip end at an closing side of the door coincides with a direction connecting a center O of the furnace shell 206 to the center of a tapping hole 210, that is, if the furnace shell 206 and the scrap bucket 201 are in such a positional relationship (the scrap bucket transported by a ceiling crane and the furnace shell are likely to be in such a positional relationship due to facility layout or the like), there arises a problem that the powdery metal material falling into the furnace shell 206 while spreading is likely to accumulate in the vicinity of the tapping hole 210 of the furnace shell 206.
In particular, in the case where the electric arc furnace 205 is an eccentric bottom tapping electric arc furnace (EBT furnace), the aforementioned problem is more likely to occur. Specifically, in the case of an EBT furnace which has the furnace shell 206 having a furnace bottom portion partially protruding outwards further than an outer surface of a circular circumferential wall portion of the furnace shell 206 in a radial direction to form a shelf-like protruding portion 208 with a small gradient, and has the tapping hole 210 (the tapping hole is blocked with a cover at the outside on a lower side of the protruding portion) provided in the protruding portion 208 while passing therethrough in a vertical direction, the aforementioned problem is more likely to occur.
The reason for this is considered that the shelf-like protruding portion 208 is likely to serves as a receiving portion for the powdery metal material.
In the drawing, a reference numeral 220 represents the accumulating powdery metal material.
It is considered that the powdery metal material 220 accumulating in the vicinity of the tapping hole 210 in such a way is seemingly easy to be melted due to its fineness. However, actually, when the powdery metal material 220 is heated, particles are surface-fused to bond each other, and turn into an ingot (sintered compact). Heat is unlikely to be transferred to the inside of the ingot. In addition, the ingot is positioned at a location distant from an electrode and hard to be melted. Therefore, there arises a problem that the ingot is likely to remain unmelted
In a case where a slag door 212 is provided at a position that is opposite to the tapping hole 210 in a radial direction, the powdery metal material is also likely to accumulate in the vicinity of the slag door 212.
The powdery metal material 222 accumulating in the vicinity of the slag door 212 is likely to cause a problem of turning into an uneasy-to-melt material (powder compact material) due to air infiltrating into the furnace or the like during the discharge of slag.
Patent Document 1 and Patent Document 2 disclose an electric arc furnace, in which the furnace shell is rotated relative to the fixed electrode.
This electric arc furnace with a rotating apparatus is intended to solve the problem of non-homogenous melting between hot spot and cold spot by rotating the furnace shell relative to the electrode to move the position of the metal material originally placed at a cold spot to a hot spot, and the metal material originally placed at a hot spot to a cold spot (for example, the furnace shell is rotated relative to the electrode by approximately 60° in a circumferential direction, whereby the electrode originally positioned in a center region in the circumferential direction of a hot spot is moved to a center region in the circumferential direction of an adjacent cold spot).
The electric arc furnace with this rotating apparatus is intended to solve the non-homogenous melting of the metal material at hot and cold spots by rotating the furnace shell relative to the electrode while the metal material is melted, and thus moving the metal material at a cold spot to a hot spot, and the metal material at a hot spot to a cold spot (the furnace shell is rotated relative to the electrode by approximately 60° in a circumferential direction, and thus the electrode, positioned in a center region of a hot spot in the circumferential direction, is moved to a center region of an adjacent cold spot in the circumferential direction).
However, these Patent Documents disclose neither the new task of the present invention nor any means for solving the problem. Therefore, they are clearly different from the present invention.
Patent Document 1: JP-A-S60-122886
Patent Document 2: JP-A-2014-40965